GB831901A - The manufacture of polyene compounds - Google Patents

Abstract

All-trans 1,14 - di - (alkoxycarbonyl) - 5,10 - dimethyltetradecaheptaene - (1,3,5,7,9,11,13)s and 1,18 - di - (alkoxycarbonyl) - 3,7,12,15 - tetramethyl - octadecanonaene - (1,3,5,7,9,11,-13,15,17)s and the corresponding compounds which contain two further methyl groups respectively in positions 1 and 14 and positions 1 and 18, are prepared by subjecting 4,9-dimethyl - dodecatetraen - (2,4,8,10) - yne - (6) - dial - (1,12) or 2,6,11,15 - tetramethyl - hexadecahexaen - (2,4,6,10,12,14) - yne - (8) - dial - (1,16) to condensation in an inert solvent, preferably methylene chloride, with an alkoxycarbonyl methylene-triphenyl-phosphine or a (1-alkoxycarbonyl ethylidene)-triphenyl-phosphine (either of which may contain alkyl or alkoxy substitution in the phenyl nuclei), splitting off triaryl-phosphine oxide from the condensation product and then partially hydrogenating and isomerizing the resulting ester at the central triple bond by hydrogenation in the presence of a lead-inhibited palladium catalyst on the one hand, and submission to heat or irradiation with light on the other hand. Alternatively the same dialkoxycarbonyl-polymers may be prepared by subjecting either of the dialdehydes to partial hydrogenation and isomerization at the triple bond by the above-described methods, condensing the resulting partially hydrogenated and isomerized compound in an inert solvent with one of the aforesaid phosphine compounds and splitting off triaryl-phosphine oxide from the condensation product. In both methods, the condensation step may be effected at room or slightly elevated temperature, the reagents being used in equivalent amounts or with excess of the triaryl phosphine reagent and an inert solvent may be present. The splitting off of the triaryl phosphine oxide from the condensate occurs on standing at room temperature and more rapidly on heating; this product may be purified by treatment with aluminium oxide. The catalytic partial hydrogenation may be effected in the presence of quinoline and an inert solvent. This yields the cis-isomer which is then isomerized to the all-trans form, if desired, in a solvent. Examples describe the preparation of the all-trans crocetine dimethyl, diethyl and dicetyl esters, all-trans bixine methyl ester and all-trans norbixine diethyl ester. The esters are useful as colouring additives to foodstuffs. The triaryl phosphine reagents may be prepared by condensing an a -halo-acetic acid alkyl ester or an a -halo-propionic acid alkyl ester with a triaryl phosphine in an inert solvent and treating the resulting phosphonium halide (e.g. bromide) with a hydrogen halide binding agent, such as a sodium alcoholate. Specifications 751,573, 756,896, 792,594 and 813,529 are referred to.